Abstract

A hot-press molding method was used to fabricate dye-doped
poly(methyl methacrylate) (PMMA) slabs. Three rhodamine
dyes, Rh640 (ClO4), Rh6G(ClO4), and
Rh6G (Cl), were impregnated into the PMMA matrix first by
dissolving the dye and granular PMMA in a solvent mixture of chloroform
and methanol and then heating the mixture in vacuo at
175 °C to obtain a spongy preform. The powdered preform was
molded into slabs at 175 °C and at <1 mbar, to eliminate the
formation of bubbles in the slabs. We annealed the slabs for
several hours to improve its optical homogeneity and hence its lasing
efficiency. When pumped by a 1.5-mJ nitrogen laser, we obtained
peak lasing efficiencies of 8% and 7.8%, respectively, for Rh6G
(ClO4) and Rh640 (ClO4) in PMMA
matrices. The lasing efficiency of Rh6G
(ClO4)-doped PMMA suffered a reduction rate of
0.012%/shot compared with 0.15%/shot for Rh640
(ClO4)-doped PMMA. In contrast, Rh6G (Cl) in a
hot-press molded PMMA slab suffered thermal bleaching that resulted in
a low lasing efficiency of <1%; this can be explained by its
absorption and fluorescence characteristics.

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